Network Working Group G. Huston
Request for Comments: 5398 December 2008
Category: Informational
Autonomous System (AS) Number Reservation for Documentation Use
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
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Abstract
To reduce the likelihood of conflict and confusion when relating
documented examples to deployed systems, two blocks of Autonomous
System numbers (ASNs) are reserved for use in examples in RFCs,
books, documentation, and the like. This document describes the
reservation of two blocks of ASNs as reserved numbers for use in
documentation.
1. Introduction
To reduce the likelihood of conflict and confusion when relating
documented examples to deployed systems, two blocks of Autonomous
System numbers (ASNs) are reserved for use in examples in RFCs,
books, documentation, and the like. This document describes the
reservation of two blocks of ASNs as reserved numbers for use in
documentation.
The problems such conflicts may cause have already been encountered
with IPv4 addresses where literal use of documented examples in a
production environment causes address and routing conflicts with
existing services. Since private-use ASNs already have a context of
use in deployed networks, these ASNs cannot be used in many example
Huston Informational [Page 1]

RFC 5398 ASN Documentation Reservation December 2008
situations. In making an explicit allocation of a set of AS numbers
reserved for documentation use, it is intended that any such
operational problems may be avoided in the future.
Similar considerations have been applied to IPv4 addresses
[IANA.IPv4], IPv6 addresses [RFC3849], and domain names [RFC2606],
and reservations have been made for similar purposes.
2. ASNs for Documentation Use
To allow documentation to accurately describe deployment examples,
the use of public or private-use AS numbers is inappropriate, and a
reserved block of AS numbers is required. This ensures that
documentation does not clash with public- or private-use AS numbers
in deployed networks, and mitigates the risks to operational
integrity of the network through inappropriate use of documentation
to perform literal configuration of routing elements on production
systems.
To allow for examples relating to the transition to use of 32-bit AS
numbers to be correctly described, a reservation of two blocks of AS
numbers is proposed in this document. One reserved block of 16
contiguous AS numbers is to lie in the range of numbers that can be
expressed as a 16-bit AS number value (i.e., values less than 65536),
and a second reserved block of 16 contiguous AS numbers is to lie in
the range of numbers that can only be expressed as 32-bit AS numbers
(values greater than 65535).
3. Operational Implications
This assignment implies that BGP operational configurations should
not peer with neighboring ASes that are numbered from this reserved
AS number set.
4. IANA Considerations
IANA has reserved a contiguous block of 16 Autonomous System numbers
from the unallocated number range within the "16-bit" number set for
documentation purposes, namely 64496 - 64511, and a contiguous block
of 16 Autonomous System numbers from the "32-bit" number set for
documentation, namely 65536 - 65551. These reservations have been
documented in the IANA AS Number Registry [IANA.AS].
5. Security Considerations
AS number reservations do not have any direct impact on Internet
infrastructure security.
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